U.S. patent application number 14/764274 was filed with the patent office on 2015-12-17 for manufacture of a moulded part.
This patent application is currently assigned to HEXCEL HOLDING GMBH. The applicant listed for this patent is HEXCEL HOLDING GMBH. Invention is credited to Johannes Moser, Joerg Radanitsch.
Application Number | 20150360426 14/764274 |
Document ID | / |
Family ID | 50179624 |
Filed Date | 2015-12-17 |
United States Patent
Application |
20150360426 |
Kind Code |
A1 |
Radanitsch; Joerg ; et
al. |
December 17, 2015 |
MANUFACTURE OF A MOULDED PART
Abstract
A method of manufacturing a laminate structure comprising
locating one or more layers of a fibrous reinforcement material
being at least partially impregnated with a curable first resin
matrix in relation to one or more layers of fibrous reinforcement
material to form a stack and subsequently infusing the stack with a
second infusion resin to cure the first and second resin.
Inventors: |
Radanitsch; Joerg;
(Pasching, AT) ; Moser; Johannes; (Pasching,
AT) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
HEXCEL HOLDING GMBH |
Pasching |
|
AT |
|
|
Assignee: |
HEXCEL HOLDING GMBH
Pasching
AT
|
Family ID: |
50179624 |
Appl. No.: |
14/764274 |
Filed: |
February 25, 2014 |
PCT Filed: |
February 25, 2014 |
PCT NO: |
PCT/EP2014/053659 |
371 Date: |
July 29, 2015 |
Current U.S.
Class: |
264/78 ;
264/257 |
Current CPC
Class: |
Y02P 70/523 20151101;
B29K 2063/00 20130101; B29C 70/443 20130101; B29K 2307/04 20130101;
B29L 2031/085 20130101; B29C 70/86 20130101; B29C 70/547 20130101;
B29K 2105/0881 20130101 |
International
Class: |
B29C 70/54 20060101
B29C070/54; B29C 70/44 20060101 B29C070/44 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 26, 2013 |
AT |
A50124/2013 |
Claims
1. A method of manufacturing a laminate structure comprising
forming a stack by locating one or more layers of a prepreg in
relation to one or more layers of resin infusible fibrous
reinforcement material, said prepreg comprising a fibrous
reinforcement material that is at least partially impregnated with
a curable first matrix resin and infusing the stack with a second
infusion resin to cure the first matrix resin and second infusion
resin.
2. A method according to claim 1, wherein the stack further
comprises a cured or partly cured fiber reinforced sheet material
comprising reinforcement, fibres and sheet material resin.
3. A method according to claim 1, wherein the stack comprises
pathways between the prepreg and/or infusible fibrous reinforcement
for conducting the second infusion resin through the stack.
4. A method according to claim 1, wherein the first matrix resin
and second infusion resin are curable at a cure temperature of 60
or 70 or 80 or 90 or 100 or 120.degree. C.
5. A method according to claim 1, wherein the second infusion resin
comprises a pigment or dye.
6. A method according to claim 1, wherein the first matrix resin
comprises an epoxy resin of EEW from 150 to 1500 said first matrix
resin being curable by an externally applied temperature in the
rare of 70.degree. C. to 110.degree. C.
7. A method according to claim 6, wherein the first matrix, resin
has an EEW in the range of from 200 to 500.
8. A method according to claim 1, wherein the first matrix resin
comprises from 0.5 to 10 wt %, based on the weight of the epoxy
resin, of one or more urea based curing agents.
9. A method according to claim 1, wherein the first matrix resin
has an onset temperature in the range of from 115 to 125.degree.
C.
10. A method according to claim 1, wherein the first matrix resin
has a dynamic enthalpy of 150 joules per gram of epoxy resin or
lower measured by DSC in accordance with ISO 11357 over
temperatures of from -40 to 270.degree. C. at 10.degree.
C./min.
11. A method according to claim 1, wherein the first matrix resin
has an 80 to 120 J/g enthalpy measured by DSC in accordance with
ISO 11357 over temperatures of from -40 to 270.degree. C. at
10.degree. C./min.
12. A method according to claim 2, wherein the cured or partly
cured fibre-reinforced sheet material comprises a sheet material
resin which comprises may comprise an epoxy-based resin, a vinyl
ester-based or a polyurethane-based resin.
13. A method according to claim 2, wherein the prepreg and/or the
cured or partly cured fibre reinforced sheet material is provided
with a surface texture to facilitate introduction of said second
infusion resin between adjacent elements of prepreg and/or cured or
partly cured fibre-reinforced sheet material.
14. A method according to claim 2, wherein the cured or partly
cured fibre reinforced material has a thickness up to 3 mm.
15. (canceled)
Description
[0001] The present invention relates to a method of making a part,
and a use, particularly but not exclusively to a method and a use
relating to the manufacture of wind turbine parts and/or
blades.
BACKGROUND
[0002] As wind turbine blades increase in size, they require stacks
of multiple layers of composite fibre and resin reinforcement.
Conventionally, resin preimpregnated fibrous reinforcement
(prepreg) is laid up in a mould to form these stacks.
Alternatively, dry fiber layers are laid up in a mould and these
are subsequently infused with a curable resin matrix using a vacuum
assisted resin transfer moulding process (VARTM).
[0003] It is known in the art that bent fibers, linear distortion,
wrinkles, or humps of fibres in a fibre-reinforced composite
material greatly degrade the mechanical properties, particularly
the strength and E-modulus, of the composite. Manufacturing of
composites with highly aligned fibres is therefore very desirable.
Particularly in VARTM lay-ups containing dry fiber layers,
maintaining fiber alignment during both lay-up and processing is a
problem.
SUMMARY OF THE INVENTION
[0004] The present invention aims to obviate or at least mitigate
the above described problem and/or to provide advantages
generally.
[0005] According to the invention, there is provided a method and a
use as defined in any of the accompanying claims.
[0006] In this way, fiber alignment can be maintained in the lay-up
or stack and linear distortion of the fibers is prevented, as the
resin preimpregnated fibrous reinforcement layers (prepreg) aid in
the alignment of the fibers.
[0007] In a further embodiment, there is provided a use of a cured
or partly cured fibre reinforced sheet material in a stack of one
or more layers of a fibrous reinforcement material being at least
partially impregnated with a curable first matrix resin forming a
prepreg, said prepreg layers being located in relation to one or
more layers of resin infusible fibrous reinforcement material to
form said stack, to prevent linear distortion of the prepreg and/or
infusible reinforcement material.
SPECIFIC DESCRIPTION
[0008] Laminate parts may be formed from any combination of one or
more layers of prepreg, dry fibrous material, and fiber reinforced
sheet material. We will now discuss aspects of each of these layers
below.
Prepreg
[0009] Prepreg is the term used to describe fibres and fabric
impregnated or in combination with a resin in the uncured state and
ready for curing. The fibres may be in the form of tows or fabrics
and a tow generally comprises a plurality of thin fibres called
filaments. The fibrous materials and resins employed in the
prepregs will depend upon the properties required of the cured
fibre reinforced material and also the use to which the cured
laminate is to be put. The fibrous material is described herein as
structural fibre. The resin may be combined with fibres or fabric
in various ways. The resin may be tacked to the surface of the
fibrous material. The resin may partially or completely impregnate
the fibrous material. The resin may impregnate the fibrous material
so as to provide a pathway to facilitate the removal of air or gas
during processing of the prepreg material.
[0010] One preferred family of resins for use in such applications
are curable epoxy resins and curing agents and curing agent
accelerators are usually included in the resin to shorten the cure
cycle time. Epoxy resins are highly suitable resins although they
can be brittle after cure causing the final laminate to crack or
fracture upon impact and it is therefore common practice to include
toughening materials such as thermoplastics or rubbers in the epoxy
resin.
[0011] The cure cycles employed for curing prepregs and stacks of
prepregs are a balance of temperature and time taking into account
the reactivity of the resin and the amount of resin and fibre
employed. The same applies to the resin infusion of dry fibrous
layers.
[0012] From an economic point of view it is desirable that the
cycle time be as short as possible and so curing agents and
accelerators are usually included in the epoxy resin. As well as
requiring heat to initiate curing of the resin the curing reaction
itself can be highly exothermic and this needs to be taken into
account in the time/temperature curing cycle in particular for the
curing of large and thick stacks of prepregs as is increasingly the
case with the production of laminates for industrial application
where large amounts of epoxy resin are employed and high
temperatures can be generated within the stack due to the exotherm
of the resin curing reaction. Excessive temperatures are to be
avoided as they can damage the mould reinforcement or cause some
decomposition of the resin. Excessive temperatures can also cause
loss of control over the cure of the resin leading to run away
cure.
[0013] Generation of excessive temperatures can be a greater
problem when thick sections comprising many layers of prepreg are
to be cured as is becoming more prevalent in the production of
fibre reinforced laminates for heavy industrial use such as in the
production of wind turbine structures particularly wind turbine
spars and shells from which the blades are assembled. In order to
compensate for the heat generated during curing it has been
necessary to employ a dwell time during the curing cycle in which
the moulding is held at a constant temperature for a period of time
to control the temperature of the moulding and is cooled to prevent
overheating this increases cycle time to undesirably long cycle
times of several hours in some instances more than eight hours.
[0014] For example a thick stack of epoxy based prepregs such as 60
or more layers can require cure temperatures above 100.degree. C.
for several hours. However, the cure can have a reaction enthalpy
of 150 joules per gram of epoxy resin or more and this reaction
enthalpy brings the need for a dwell time during the cure cycle at
below 100.degree. C. to avoid overheating and decomposition of the
resin. Furthermore, following the dwell time it is necessary to
heat the stack further to above 100.degree. C. (for example to
above 125.degree. C.) to complete the cure of the resin. This leads
to undesirably long and uneconomic cure cycles. In addition, the
high temperatures generated can cause damage to the mould or bag
materials or require the use of special and costly materials for
the moulds or bags.
[0015] In addition to these problems there is a desire to produce
laminar structures from prepregs in which the cured resin has a
high glass transition temperatures (Tg) such as above 80.degree. C.
to extend the usefulness of the structures by improving their
resistance to exposure at high temperatures and/or high humidity
for extended periods of time which can cause an undesirable
lowering of the Tg. For wind energy structures a Tg above
90.degree. C. is preferred. Increase in the Tg may be achieved by
using a more reactive resin. However the higher the reactivity of
the resin the greater the heat released during curing of the resin
in the presence of hardeners and accelerators which increases the
attendant problems as previously described.
[0016] The reactivity of an epoxy resin is indicated by its epoxy
equivalent weight (EEW) the lower the EEW the higher the
reactivity. The epoxy equivalent weight can be calculated as
follows: (Molecular weight epoxy resin)/(Number of epoxy groups per
molecule). Another way is to calculate with epoxy number that can
be defined as follows: Epoxy number=100/epoxy eq.weight. To
calculate epoxy groups per molecule: (Epoxy
number.times.mol.weight)/100. To calculate mol.weight:
(100.times.epoxy groups per molecule)/epoxy number. To calculate
mol.weight: epoxy eq.weight.times.epoxy groups per molecule. The
present invention is particularly concerned with providing a
prepreg that can be based on a reactive epoxy resin that can be
cured at a lower temperature with an acceptable moulding cycle
time.
[0017] The present invention therefore provides a prepreg
comprising a mixture of a fibrous reinforcement and an epoxy resin
containing from 20% to 85% by weight of an epoxy resin of EEW from
150 to 1500 said resin being curable by an externally applied
temperature in the range of 70.degree. C. to 110.degree. C.
[0018] In an embodiment of the present invention therefore provides
a prepreg comprising a mixture of a fibrous reinforcement and an
epoxy resin containing from 20% to 85% by weight of an epoxy resin
of EEW from 150 to 1500 said resin being curable by an externally
applied temperature in the range of 70.degree. C. to 110.degree.
C., wherein the resin contains from 0.5 to 5 wt % of a urea curing
agent, and the resin is cured in the absence of a dicyandiamide
based hardener.
[0019] We have found that prepreg and its epoxy resin matrix has a
reduced cure time, whilst providing good mechanical performance, a
desirable Tg (glass transition temperature) and good mechanical
performance in combination with the fibrous reinforcement of the
prepreg. In a preferred embodiment the curing resin has a dynamic
enthalpy of 150 joules per gram of epoxy resin or lower. This resin
may be cured in less than ten hours, and preferably less than 8
hours.
[0020] This renders the prepreg as described herein particularly
suitable to lay-ups in combination with dry fibrous layers and/or
cured fiber reinforced sheet materials which are subsequently
infused with a further resin.
[0021] We have found that such desirable prepregs and stacks of
prepregs may be obtained using conventionally available epoxy
resins if the epoxy resin is cured in the absence of a traditional
hardener such as dicyandiamide and in particular we have found that
these desirable prepregs can be obtained by use of a urea based
curing agent in the absence of a hardener such as dicyandiamide.
The relative amount of the curing agent and the epoxy resin that
should be used will depend upon the reactivity of the resin and the
nature and quantity of the fibre reinforcement in the prepreg.
Typically from 0.5 to 10 wt % of the urea based curing agent based
on the weight of epoxy resin is used.
[0022] The epoxy resin has a high reactivity as indicated by an EEW
in the range from 150 to 1500 preferably a high reactivity such as
an EEW in the range of from 200 to 500 and the resin composition
comprises the resin and an accelerator or curing agent. Suitable
epoxy resins may comprise blends of two or more epoxy resins
selected from monofunctional, difunctional, trifunctional and/or
tetrafunctional epoxy resins.
[0023] Suitable difunctional epoxy resins, by way of example,
include those based on: diglycidyl ether of bisphenol F, diglycidyl
ether of bisphenol A (optionally brominated), phenol and cresol
epoxy novolacs, glycidyl ethers of phenol-aldelyde adducts,
glycidyl ethers of aliphatic diols, diglycidyl ether, diethylene
glycol diglycidyl ether, aromatic epoxy resins, aliphatic
polyglycidyl ethers, epoxidised olefins, brominated resins,
aromatic glycidyl amines, heterocyclic glycidyl imidines and
amides, glycidyl ethers, fluorinated epoxy resins, glycidyl esters
or any combination thereof.
[0024] Difunctional epoxy resins may be selected from diglycidyl
ether of bisphenol F, diglycidyl ether of bisphenol A, diglycidyl
dihydroxy naphthalene, or any combination thereof.
[0025] Suitable trifunctional epoxy resins, by way of example, may
include those based upon phenol and cresol epoxy novolacs, glycidyl
ethers of phenol-aldehyde adducts, aromatic epoxy resins, aliphatic
triglycidyl ethers, dialiphatic triglycidyl ethers, aliphatic
polyglycidyl amines, heterocyclic glycidyl imidines and amides,
glycidyl ethers, fluorinated epoxy resins, or any combination
thereof. Suitable trifunctional epoxy resins are available from
Huntsman Advanced Materials (Monthey, Switzerland) under the
tradenames MY0500 and MY0510 (triglycidyl paraaminophenol) and
MY0600 and MY0610 (triglycidyl meta-aminophenol). Triglycidyl
meta-aminophenol is also available from Sumitomo Chemical Co.
(Osaka, Japan) under the tradename ELM-120.
[0026] Suitable tetrafunctional epoxy resins include N,N,
N',N'-tetraglycidyl-methylenediamine (available commercially from
Mitsubishi Gas Chemical Company under the name Tetrad-X, and as
Erisys GA-240 from CVC Chemicals), and
N,N,N',N'-tetraglycidylmethylenedianiline (e.g. MY0720 and MY0721
from Huntsman Advanced Materials). Other suitable multifunctional
epoxy resins include DEN438 (from Dow Chemicals, Midland, Mich.)
DEN439 (from Dow Chemicals), Araldite ECN 1273 (from Huntsman
Advanced Materials), and Araldite ECN 1299 (from Huntsman Advanced
Materials).
[0027] The epoxy resin composition also comprises one or more urea
based curing agents and it is preferred to use from 0.5 to 10 wt %
based on the weight of the epoxy resin of a curing agent, more
preferably 1 to 8 wt %, more preferably 2 to 8 wt %, more
preferably 0.5 to 5 wt %, more preferably 0.5 to 4 wt % inclusive,
or most preferably 1.3 to 4 wt % inclusive.
[0028] The prepregs of this invention are typically used at a
different location from where they are manufactured and they
therefore require handleability. It is therefore preferred that
they are dry or as dry as possible and have low surface tack. It is
therefore preferred to use high viscosity resins. This also has the
benefit that the impregnation of the fibrous layer is slow allowing
air to escape and to minimise void formation.
[0029] The urea curing agent may comprise a bis urea curing agent,
such as 2,4 toluene bis dimethyl urea or 2,6 toluene bis dimethyl
urea and/or combinations of the aforesaid curing agents. Urea based
curing agents may also be referred to as "urones".
[0030] Preferred urea based materials are the range of materials
available under the commercial name DYHARD.RTM. the trademark of
Alzchem, urea derivatives, which include bis ureas such as UR500
and UR505.
[0031] In an embodiment of the invention, the prepreg may comprise
a resin system comprising an epoxy resin containing from 20% to 85%
by weight of an epoxy of EEW from 150 to 1500, and 0.5 to 10 wt %
of a curing agent, the resin system comprising an onset temperature
in the range of from 115 to 125.degree. C., and/or a peak
temperature in the range of from 140 to 150.degree. C., and/or an
enthalpy in the range of from 80 to 120 J/g (T.sub.onset,
T.sub.peak, Enthalpy measured by DSC(=differential scanning
calorimetry) in accordance with ISO 11357, over temperatures of
from -40 to 270.degree. C. at 10.degree. C./min). T.sub.onset is
defined as the onset-temperature at which curing of the resin
occurs during the DSC scan, whilst T.sub.peak is defined as the
peak temperature during curing of the resin during the scan.
[0032] The resin system is particularly suitable for prepreg
applications at which a desired cure temperature is below
100.degree. C. The resin system may be processed to cure over a
wide processing temperature range, ranging from 75.degree. C. up to
120.degree. C. Due to its low exothermic properties this resin can
be used for large industrial components, suitable for the cure of
thin and thick sections. It demonstrates a good static and dynamic
mechanical performance following cure temperatures <100.degree.
C.
[0033] The structural fibres employed in lay-up both in the
prepregs and as dry fibre reinforcement may be in the form of
random, knitted, non-woven, multi-axial or any other suitable
pattern. For structural applications, it is generally preferred
that the fibres be unidirectional in orientation. When
unidirectional fibre layers are used, the orientation of the fibre
can vary throughout the prepreg stack. However, this is only one of
many possible orientations for stacks of unidirectional fibre
layers. For example, unidirectional fibres in neighbouring layers
may be arranged orthogonal to each other in a so-called
0/90.degree. arrangement, which signifies the angles between
neighbouring fibre layers. Other arrangements, such as
0/+45/-45/90.degree. are of course possible, among many other
arrangements.
[0034] The structural fibres may comprise cracked (i.e.
stretch-broken), selectively discontinuous or continuous fibres.
The structural fibres may be made from a wide variety of materials,
such as carbon, graphite, glass, metalized polymers, aramid and
mixtures thereof. Glass and carbon fibres are preferred carbon
fibre, being preferred for wind turbine shells of length above 40
metres such as from 50 to 60 metres. The structural fibres, may be
individual tows made up of a multiplicity of individual fibres and
they may be woven or non-woven fabrics. The fibres may be
unidirectional, bidirectional or multidirectional according to the
properties required in the final laminate. Typically the fibres
will have a circular or almost circular cross-section with a
diameter in the range of from 3 to 20 .mu.m, preferably from 5 to
12 .mu.m. Different fibres may be used in different prepregs used
to produce a cured laminate.
[0035] Exemplary layers of unidirectional structural fibres are
made from HexTow.RTM. carbon fibres, which are available from
Hexcel Corporation. Suitable HexTow.RTM. carbon fibres for use in
making unidirectional fibre layers include: IM7 carbon fibres,
which are available as fibres that contain 6,000 or 12,000
filaments and weight 0.223 g/m and 0.446 g/m respectively; IM8-IM10
carbon fibres, which are available as fibres that contain 12,000
filaments and weigh from 0.446 g/m to 0.324 g/m; and AS7 carbon
fibres, which are available in fibres that contain 12,000 filaments
and weigh 0.800 g/m.
[0036] The structural fibres of the prepregs will be substantially
impregnated with the epoxy resin and prepregs with a resin content
of from 20 to 85 wt % of the total prepreg weight are preferred.
The prepregs of the present invention are predominantly composed of
resin and structural fibres.
[0037] The stacks of prepregs and dry fiber layers of this
invention may contain more than 40 layers, typically more than 60
layers and at times more than 80 layers. Typically the stack will
have a thickness of from 35 to 100 mm.
Fiber Materials
[0038] As discussed, the fiber materials suitable for resin
infusion contain unimpregnated fibers. These layers may comprise
structural fibers in the form of random, knitted, non-woven,
multi-axial or any other suitable pattern. For structural
applications, it is generally preferred that the fibres be
unidirectional in orientation. When unidirectional fibre layers are
used, the orientation of the fibre can vary throughout the prepreg
stack. However, this is only one of many possible orientations for
stacks of unidirectional fibre layers. For example, unidirectional
fibres in neighbouring layers may be arranged orthogonal to each
other in a so-called 0/90 arrangement, which signifies the angles
between neighbouring fibre layers. Other arrangements, such as
0/+45/-45/90 are of course possible, among many other
arrangements.
[0039] The structural fibres may comprise cracked (i.e.
stretch-broken), selectively discontinuous or continuous fibres.
The structural fibres may be made from a wide variety of materials,
such as carbon, graphite, glass, metalized polymers, aramid and
mixtures thereof. Glass and carbon fibres are preferred. Carbon
fibre, being preferred for wind turbine shells of length above 40
metres such as from 50 to 60 metres. The structural fibres, may be
individual tows made up of a multiplicity of individual fibres and
they may be woven or non-woven fabrics. The fibres may be
unidirectional, bidirectional or multidirectional according to the
properties required in the final laminate. Typically the fibres
will have a circular or almost circular cross section with a
diameter in the range of from 3 to 20 .mu.m, preferably from 5 to
12 .mu.m. Different fibres may be used in different prepregs used
to produce a cured laminate.
[0040] Exemplary layers of unidirectional structural fibres are
made from HexTow.RTM. carbon fibres, which are available from
Hexcel Corporation. Suitable HexTow.RTM. carbon fibres for use in
making unidirectional fibre layers include: IM7 carbon fibres,
which are available as fibres that contain 6,000 or 12,000
filaments and weight 0.223 g/m and 0.446 g/m respectively; IM8-IM10
carbon fibres, which are available as fibres that contain 12,000
filaments and weigh from 0.446 g/m to 0.324 g/m; and AS7 carbon
fibres, which are available in fibres that contain 12,000 filaments
and weigh 0.800 g/m.
[0041] Preferably, the dry fiber material comprises glass fiber
material. The dry fibre material preferably has an area weight in
the range of from 400 to 2500 g/m.sup.2, preferably from 600 to
2400 g/m.sup.2, and more preferably from 1000 to 1200 g/m.sup.2.
The glass fiber material may comprise glass fiber filaments having
a diameter in the range of from 1 to 20 .mu.m, preferably from 10
to 15 .mu.m. We have found that these relatively large diameter
filaments aid resin infusion. This is particularly important for
large structure such as for wind turbine blades or parts
thereof.
Fiber Reinforced Sheet Material
[0042] Advantageously, the lay-up may contain one or more partially
or fully cured layers of a fiber reinforced sheet material.
[0043] In an embodiment of the invention the fibre reinforced sheet
material may contain regions of fully cured resin adjacent to
regions of uncured, partially cured resin or unimpregnated fibre. A
fibre reinforced sheet material comprising fully cured and
non-fully cured regions of resin provides improved integration into
the cured stack.
[0044] The use of partially or fully cured fibre-reinforced sheet
material allows for very high fibre content and highly aligned
fibres in the sheets. Furthermore, the fact that the sheet is cured
facilitates transportation of the sheets, as no special conditions,
such as temperature range or humidity range, are required. In
addition, the combination of the sheet shape with the cured state
facilitates adjustment of the sheets to the shape of the mould
without compromising the alignment, or in other words the
straightness, of the fibres in the lay-up forming the composite
member or part. This is particularly important to complex shapes
such as an airfoil of wind turbine blade, where the desired fibre
distribution is a complicated three-dimensional shape.
[0045] Elements of a desired shape may be cut from the sheet
material to facilitate a particular lay-up to form a composite
member or part.
[0046] In a highly preferred embodiment of the invention, at least
some of the elements of cured fibre-reinforced sheet material are
positioned as partially overlapping tiles so that a number of
substantially parallel element edges are provided. This allows for
positioning of the elements very close to the surface of the mould,
and by adjusting the overlapping area between elements, almost any
desired overall distribution of reinforcing fibres may be realised.
Particularly, the elements may be positioned in a cross section of
a wind turbine blade so that the fibres substantially resemble the
distribution of water in a lake having a depth profile
corresponding to the distance from the centreline of the blade to
the surface of the cross section. In a particularly preferred
embodiment, the substantially parallel element edges are edges,
which are substantially parallel to the length of the elements of
cured fibre-reinforced sheet material. This leads to a relatively
short resin introduction distance and hence easier manufacturing
and greater reproducibility
[0047] The elements of cured fibre-reinforced sheet material may be
provided along a shorter or a larger fraction of the length of the
composite structure. However, it is typically preferred that the
elements are positioned along at least 75% of the length of the
wind turbine blade shell member, and in many cases it is more
preferred that the cured fibre-reinforced sheet material is
positioned along at least 90% of the length of the composite
structure
[0048] The cured fibre-reinforced sheet material comprises fibres,
such as carbon fibres, glass fibres, aramid fibres, natural fibres,
such as cellulose-based fibre like wood fibres, organic fibres or
other fibres, which may be used for reinforcement purposes. In a
preferred embodiment, the fibres are unidirectional fibres oriented
parallel to the length of the cured fibre-reinforced sheet
material. This provides for very high strength and stiffness in the
length of the cured fibre-reinforced sheet material. Other
orientations or combinations of orientations may be suitable in
some applications. Examples of other suitable orientations are
bi-axial fibres oriented at +-45.degree., +-30.degree., or
0-90.degree. relative to the length of the sheet material; and
triaxial fibres oriented at +-45.degree. and in the length of the
sheet material. Such orientations increase the edgewise and/or
twisting strength and stiffness of the composite material.
[0049] The structural fibres may comprise cracked (i.e.
stretch-broken), selectively discontinuous or continuous fibres.
The structural fibres may be made from a wide variety of materials,
such as carbon, graphite, glass, metalized polymers, aramid and
mixtures thereof. Glass and carbon fibres are preferred carbon
fibre, being preferred for wind turbine shells of length above 40
metres such as from 50 to 60 metres. The structural fibres, may be
individual tows made up of a multiplicity of individual fibres and
they may be woven or non-woven fabrics. The fibres may be
unidirectional, bidirectional or multidirectional according to the
properties required in the final laminate. Typically the fibres
will have a circular or almost circular cross-section with a
diameter in the range of from 3 to 20 .mu.m, preferably from 5 to
12 .mu.m. Different fibres may be used in different prepregs used
to produce a cured laminate.
[0050] Exemplary layers of unidirectional structural fibres are
made from HexTow.RTM. carbon fibres, which are available from
Hexcel Corporation. Suitable HexTow.RTM. carbon fibres for use in
making unidirectional fibre layers include: IM7 carbon fibres,
which are available as fibres that contain 6,000 or 12,000
filaments and weight 0.223 g/m and 0.446 g/m respectively; IM8-IM10
carbon fibres, which are available as fibres that contain 12,000
filaments and weigh from 0.446 g/m to 0.324 g/m; and AS7 carbon
fibres, which are available in fibres that contain 12,000 filaments
and weigh 0.800 g/m.
[0051] Furthermore, the cured fibre-reinforced sheet material
comprises a sheet material resin, preferably a thermosetting resin,
such as an epoxy-based, a vinyl ester-based resin, a
polyurethane-based or another suitable thermosetting resin. The
cured fibre reinforced sheet material may comprise more than one
type of resin and more than one type of fibres In a preferred
embodiment, the cured fibre-reinforced sheet material comprises
unidirectional carbon fibres and an epoxy-based resin or a vinyl
ester-based resin, preferably the cured fibre-reinforced sheet
material consist substantially of unidirectional carbon fibres and
an epoxy-based resin.
[0052] The resin material may comprise an epoxy resin having an
epoxy equivalent weight in the range of from 50 to 250, preferably
from 100 to 200, and an amine hardener, the resin material being
in-line curable.
[0053] The reactivity of an epoxy resin is indicated by its epoxy
equivalent weight (EEW) the lower the EEW the higher the
reactivity. The epoxy equivalent weight can be calculated as
follows: (Molecular weight epoxy resin)/(Number of epoxy groups per
molecule). Another way is to calculate with epoxy number that can
be defined as follows: Epoxy number=100/epoxy eq.weight. To
calculate epoxy groups per molecule: (Epoxy
number.times.mol.weight)/100. To calculate mol.weight:
(100.times.epoxy groups per molecule)/epoxy number. To calculate
mol.weight: epoxy eq.weight.times.epoxy groups per molecule. The
present invention is particularly concerned with providing a
prepreg that can be based on a reactive epoxy resin that can be
cured at a lower temperature with an acceptable moulding cycle
time.
[0054] The epoxy resin has a high reactivity as indicated by an EEW
in the range from 150 to 1500 preferably a high reactivity such as
an EEW in the range of from 200 to 500 and the resin composition
comprises the resin and an accelerator or curing agent. Suitable
epoxy resins may comprise blends of two or more epoxy resins
selected from monofunctional, difunctional, trifunctional and/or
tetrafunctional epoxy resins.
[0055] Suitable difunctional epoxy resins, by way of example,
include those based on: diglycidyl ether of bisphenol F, diglycidyl
ether of bisphenol A (optionally brominated), phenol and cresol
epoxy novolacs, glycidyl ethers of phenol-aldelyde adducts,
glycidyl ethers of aliphatic diols, diglycidyl ether, diethylene
glycol diglycidyl ether, aromatic epoxy resins, aliphatic
polyglycidyl ethers, epoxidised olefins, brominated resins,
aromatic glycidyl amines, heterocyclic glycidyl imidines and
amides, glycidyl ethers, fluorinated epoxy resins, glycidyl esters
or any combination thereof.
[0056] Difunctional epoxy resins may be selected from diglycidyl
ether of bisphenol F, diglycidyl ether of bisphenol A, diglycidyl
dihydroxy naphthalene, or any combination thereof.
[0057] Suitable trifunctional epoxy resins, by way of example, may
include those based upon phenol and cresol epoxy novolacs, glycidyl
ethers of phenol-aldehyde adducts, aromatic epoxy resins, aliphatic
triglycidyl ethers, dialiphatic triglycidyl ethers, aliphatic
polyglycidyl amines, heterocyclic glycidyl imidines and amides,
glycidyl ethers, fluorinated epoxy resins, or any combination
thereof. Suitable trifunctional epoxy resins are available from
Huntsman Advanced Materials (Monthey, Switzerland) under the
tradenames MY0500 and MY0510 (triglycidyl paraaminophenol) and
MY0600 and MY0610 (triglycidyl meta-aminophenol). Triglycidyl
meta-aminophenol is also available from Sumitomo Chemical Co.
(Osaka, Japan) under the tradename ELM-120.
[0058] Suitable tetrafunctional epoxy resins include N,N,
N',N'-tetraglycidyl-mxylenediamine (available commercially from
Mitsubishi Gas Chemical Company under the name Tetrad-X, and as
Erisys GA-240 from CVC Chemicals), and
N,N,N',N'-tetraglycidylmethylenedianiline (e.g. MY0720 and MY0721
from Huntsman Advanced Materials). Other suitable multifunctional
epoxy resins include DEN438 (from Dow Chemicals, Midland, Mich.)
DEN439 (from Dow Chemicals), Araldite ECN 1273 (from Huntsman
Advanced Materials), and Araldite ECN 1299 (from Huntsman Advanced
Materials).
[0059] The cured fibre-reinforced sheet material is a relatively
flat member having a length, which is at least ten times the width,
and a width, which is at least 5 times the thickness of the sheet
material. Typically, the length is 20-50 times the width or more
and the width is 20 to 100 times the thickness or more. In a
preferred embodiment, the shape of the sheet material is
band-like.
[0060] It is preferred that the cured fibre-reinforced sheet
material is dimensioned such that it is coilable. By coilable is
meant that the sheet material may be coiled onto a roll having a
diameter that allows for transportation in standard size
containers. This greatly reduces the manufacturing cost of the
composite member, as endless coils of the cured fibre-reinforced
sheet material may be manufactured at a centralised facility and
shipped to the blade assembly site, where it may be divided into
elements of suitable size. To further enhance shipping, it is
preferred that the thickness of the cured fibre-reinforced sheet
material is chosen so that the cured fibre-reinforced sheet
material may be coiled onto a roll with a diameter of less than 2 m
based on the flexibility, stiffness, fibre type and fibre content
utilised. Typically, this corresponds to a thickness up to 3.0 mm,
however, for high fibre contents and stiffness, a thickness below
2.5 mm is usually more suitable On the other hand, the thick sheet
materials provide for rather large steps at the outer surface,
which favours the thinner sheet materials. However, the sheet
materials should typically not be thinner than 0.5 mm as a large
number of sheets then would be needed leading to increased
manufacturing time. In a preferred embodiment, the thickness of the
cured fibre-reinforced sheet material is about 15 to 2 mm.
[0061] The width of the cured fibre-reinforced sheet material
typically varies along the length of the sheet material. Typically,
the maximum width should be more than 100 mm and to reduce the
number of sheets, a width of more than 150 mm is desirable.
Experimental work has shown that in many cases, the width may
preferably be more than 200 mm at the widest place. On the other
hand, the resin must travel between adjacent sheets in length
corresponding to the width of the sheet and hence the maximum width
of the sheet material is preferably less than 500 mm to allow for
suitable control of resin introduction. In a preferred embodiment,
the maximum width is less than 400 mm and for example if the resin
is selected so that it initiates curing prior to complete infusion,
it is preferred that the maximum sheet width is less than about 300
mm.
[0062] In a preferred embodiment of the method according to the
invention, the cured fibre reinforced sheet material is pre-treated
before being positioned in the mould. Examples of pre-treatment is
sandblasting, e.g. to increase the mechanical binding with the
resin or to change the surface texture (see below), rinsing of the
surfaces by mechanical and/or chemical means or acclimatising, e g.
drying or heating. More than one type of pre-treatment of the cured
fibre-reinforced sheet material may be suitable dependent on the
conditions of the use.
[0063] The cured fibre-reinforced sheet material comprises highly
aligned fibres and the cured fibre-reinforced sheet material may
therefore advantageously be a pultruded cured composite material or
a belt pressed cured composite. These techniques may provide the
desired sheet shapes with a high fibre content of highly aligned
fibres. Furthermore, these techniques are particularly suitable for
manufacturing of endless lengths of material which are cut to the
desired lengths.
[0064] The sheet material may have the following properties (refers
to measurement standard):
TABLE-US-00001 Fibre volume fraction (%) 57 to 60; Tensile strength
(ISO527-5) (MPa) 1600 to 2000; Tensile modulus (ISO527-5) (GPa) 120
to 150; Tensile elongation (ISO527-5) (%) 1.20 to 1.33 Flexural
strength (ISO527-5) (MPa) 2100 to 2200; Flexural modulus (EN2562)
(GPa) 120 to 150; Interlaminar shear strength (EN2563) (MPa) 90 to
100; Compression strength (ASTM D6641) (MPa) 1200 to 1300;
Compression modulus (ASTM D6641) (GPa) 120 to 130; Elongation (ASTM
D6641) (%) 0.99
[0065] The fiber volume fraction is the volume of the sheet
material that is occupied by the fibers. The sheet may have an
areal weight in the range of from 2000 to 4000 g/m.sup.2,
preferably from 2200 to 2800 g/m.sup.2, more preferably 1500
g/m.sup.2. The Tg of the resin matrix may be 100 to 150.degree. C.,
preferably 110 to 140.degree. C., more preferably 110 to
130.degree. C.
[0066] The resin materials of the cured sheet material, prepreg and
infusion resin are compatible with each other. Suitable
combinations of resins are listed in the below Table 1. Preferably,
the prepreg resin, sheet layer resin and infusion resin are all of
the same resin type. More preferably, the prepreg resin and
infusion resin are an epoxy resin and the sheet layer resin is a
vinylester resin. All conventional types of resin or combinations
of resins can be used, however, since they mix they should be
compatible. Any resin suitable for use in the laminate is suitable
for use in the prepreg and vice versa. The resins should be
selected so that a good bond is formed between the cured sheet
material and the infused resin and/or prepreg resin. A good bond
can be determined by performing mechanical testing on cured parts,
using established testing methods.
TABLE-US-00002 TABLE 1 Component Resin Type Reinforcement Prepreg
Resin Epoxy Prepreg Reinforcement Sheet layer Epoxy, Polyester,
Sheet Vinyl Ester, Poly Reinforcement urethane Infused Component
Epoxy Dry reinforcement
Processing and Curing
[0067] As discussed the materials are laid up in a mould in a
desired sequence. The material may comprise combinations of one or
more layers of prepreg, dry reinforcement and/or reinforced sheet
materials.
[0068] Curing at a pressure close to atmospheric pressure can be
achieved by the so-called vacuum bag technique. This involves
placing the lay up stack in an air-tight bag and creating a vacuum
on the inside of the bag. The bag may be placed in or over a mould
prior or after creating the vacuum.
[0069] Infusion resin is supplied to the dry fiber layers by
suitable conduits. The infusion resin or second infusion resin is
drawn through the dry fibers by the reduced pressure inside the
bag.
[0070] The first matrix resin inside the prepreg and the second
infusion resin are then cured by externally applied heat to produce
the moulded laminate or part. The use of the vacuum bag has the
effect that the stack experiences a consolidation pressure of up to
atmospheric pressure, depending on the degree of vacuum
applied.
[0071] Upon curing, the stack becomes a composite laminate,
suitable for use in a structural application, such as for example
an automotive, marine vehicle or an aerospace structure or a wind
turbine structure such as a shell for a blade or a spar. Such
composite laminates can comprise structural fibres at a level of
from 80% to 15% by volume, preferably from 58% to 65% by
volume.
[0072] The invention has applicability in the production of a wide
variety of materials. One particular use is in the production of
wind turbine blades. Typical wind turbine blades comprise two long
shells which come together to form the outer surface of the blade
and a supporting spar within the blade and which extends at least
partially along the length of the blade. The shells and the spar
may be produced by curing the prepreg/dry fiber stacks of the
present invention.
[0073] Advantageously the addition of cured sheet material to the
stack reduces the peak temperature achieved during cure. Because
the cured sheet material is precured it does not exotherm, instead
it increases the total heat capacity of the stack. It can therefore
be used in thick stacks to prevent high temperatures from being
reached during cure which would otherwise damage the cured
stack.
[0074] The length and shape of the shells vary but the trend is to
use longer blades (requiring longer shells) which in turn can
require thicker shells and a special sequence of materials within
the stack to be cured. This imposes special requirements on the
materials from which they are prepared. Carbon fibre based prepregs
are preferred for blades of length 30 metres or more particularly
those of length 40 metres or more such as 45 to 65 metres whilst
the dry fiber is preferably a glass fiber. The length and shape of
the shells may also lead to the use of different prepregs/dry fiber
materials within the stack from which the shells are produced and
may also lead to the use of different prepregs/dry fiber
combinations along the length of the shell.
[0075] During vacuum assisted processing and curing, it may be very
difficult to introduce resin between sheets of dry fiber material
if the sheets are positioned very close. This is particularly the
case if the space between the sheets is also subjected to
vacuum.
[0076] In a preferred embodiment of the invention, the prepreg
and/or the cured fibre reinforced sheet material is provided with a
surface texture to facilitate introduction of resin between
adjacent elements of prepreg and/or cured fibre-reinforced sheet
material. The surface texture may comprise resin protrusions of a
height above a main surface of the cured fibre-reinforced sheet
material, preferably in the order of about 0.1 mm to 0.5 mm,
preferably from 0.5 to 3 mm, but larger protrusions may in some
cases, such as when the resin introduction distance is relatively
large, be larger. The resin protrusions may be uncured, cured or
partially cured.
[0077] The surface texture may in addition to this or as an
alternative comprise recesses, such as channels into the main
surface of the cured fibre-reinforced sheet material, preferably
the recesses are in the order of 0.1 mm to 0.5 mm below the main
surface, but in some cases larger recesses may be suitable.
Typically, the protrusions and/or recesses are separated by 1 cm to
2 cm and/or by 0.5 to 4 cm, but the spacing may be wider or smaller
dependent on the actual size of the corresponding protrusions
and/or recesses.
[0078] Surface texture of the types described above may be provided
after the manufacturing of the cured fibre-reinforced sheet
material, e.g. by sanding, sand blasting, grinding or dripping of
semi-solid resin onto the surface. But it is preferred that the
surface texture to facilitate introduction of resin between
adjacent elements of cured fibre-reinforced sheet material at least
partially is provided during manufacturing of the cured
fibre-reinforced sheet material. This is particularly easily made
when the cured fibre-reinforced sheet material is manufactured by
belt pressing, as the surface texture may be derived via a negative
template on or surface texture of the belt of the belt press. In
another embodiment, a foil is provided between the belt and the
fibre-reinforced sheet material is formed in the belt press. Such a
foil may also act as a liner and should be removed prior to
introduction of the cured fibre reinforced sheet material in the
mould.
[0079] In a preferred embodiment, the facilitating effect of
surface texture on the resin distribution during resin introduction
is realised by providing a plurality of inner spacer elements
between adjacent elements of the cured fibre-reinforced sheet
material. The inner spacer elements may advantageously be selected
from one or more members of the group consisting of a collection of
fibres, such as glass fibres and/or carbon fibres, a solid
material, such as sand particles, and a high melting point polymer,
e.g. as dots or lines of resin. It is preferred that the inner
spacer elements are inert during the resin introduction, and for
example does not change shape or react with the introduced resin.
Using inner spacer elements may be 15 advantageous in many cases,
as it does not require any particular method of manufacturing of
the cured fibre-reinforced sheet material or a special
pre-treatment of the cured fibre-reinforced sheet material. The
inner spacing elements are preferably in the size range of 0.1 mm
to 0.5 mm and separated by typically 1 cm to 2 cm, but both the
sizes and the spaces may be suitable in some cases. Typically, the
larger the inner spacing element, the larger the spacing can be
allowed.
[0080] Alternatively, one or more suitable spacers may be used to
space the dry fibre material layers. A suitable space may comprise
silicon paper. This may layer be removed following processing and
curing of the stack.
[0081] As discussed, to facilitate the introduction of resin this
process may advantageously be vacuum assisted. The method may
comprise the step of forming a vacuum enclosure around the
composite structure. The vacuum enclosure may preferably be formed
by providing a flexible second mould part in vacuum tight
communication with the mould. Thereafter a vacuum may be provided
in the vacuum enclosure by a vacuum means, such as a pump in
communication with the vacuum enclosure so that the resin may be
introduced by a vacuum assisted process, such as vacuum assisted
resin transfer moulding, VARTM. A vacuum assisted process is
particularly suitable for large structures, such as wind turbine
blade shell members, as long resin transportation distances could
otherwise lead to premature curing of the resin, which could
prevent further infusion of resin. Furthermore, a vacuum assisted
process will reduce the amount of air in the wind turbine blade
shell member and hence reduce the presence of air in the infused
composite, which increases the strength and the
reproducibility.
[0082] The infusion resin must have a sufficiently low viscosity to
achieve a complete infusion. Preferably the uncured resin has a
viscosity between 100 and 200 cPoise, preferably from 120 to 140
upon mixing at 25.degree. C. More specifically, the initial mix
viscosity of the (infusion) resin may vary at 25.degree. C. between
50 cPoise (ultralow viscosity resins) and 140 cPoise. After 4 hours
at 25.degree. C. the viscosity would be preferably be between 500
to 1000 cPoise, preferably between 550 to 650 cPoise. Preferably
the infusion resin is an epoxy resin
[0083] The infusion resin may be curable at temperatures of from 60
to 100.degree. C., preferably from 60 to 90.degree. C., more
preferably from 80 to 100.degree. C. The resin may have a viscosity
during the infusion phase of from 50 to 200 mPas, preferably from
100 to 160 mPas and more preferably of from 120 to 150 mPas. The
neat infusion resin may have a density ranging of from 1.1 to 1.20
g/cm.sup.3; a flexural strength of from 60 to 150 N/mm2, preferably
from 90 to 140 N/mm.sup.2; an elasticity modulus of from 2.5 to 3.3
kN/mm2, preferably from 2.8 to 3.2 kN/mm.sup.2; a tensile strength
of from 60 to 80 N/mm.sup.2, preferably from 70 to 80 N/mm.sup.2; a
compressive strength of from 50 to 100 N/mm.sup.2; elongation at
break of from 4 to 20%, preferably from 8 to 16% and/or
combinations of the aforesaid properties.
[0084] An example of a suitable epoxy infusion resin is Epikote MGS
RIM 135, as supplied by Hexion.
[0085] Composite parts or members according to the invention or
manufactured by the method according to the invention may either
form a wind turbine blade shell individually or form a wind turbine
blade shell when connected to one or more further such composite
members, e.g. by mechanical fastening means and/or be adhesive.
From such wind turbine blade shells, a wind turbine blade may
advantageously be 16 manufactured by connecting two such wind
turbine blade shells by adhesive and/or mechanical means, such as
by fasteners. Both the wind turbine blade shell and the combined
wind turbine blade may optionally comprise further elements, such
as controlling elements, lightning conductors, etc. In a
particularly preferred embodiment, each blade shell consists of a
composite member manufacturable by the method according to the
invention. In another preferred embodiment, the wind turbine blade
shell member manufactured by the method according to the invention
forms substantially the complete outer shell of a wind turbine
blade, i.e. a pressure side and a suction side which are formed
integrally during manufacturing of the wind turbine blade shell
member.
[0086] One aspect of the invention concerns a wind turbine blade
comprising prepreg, resin infused dry fiber material and cured
fibre-reinforced sheet material. The cured fibre reinforced sheet
material is may be positioned near the outer surface of the blade
as partially overlapping tiles.
[0087] In a preferred embodiment the cured fibre-reinforced sheet
material is pultruded or band pressed cured fibre-reinforced sheet
material and has been divided into elements of cured
fibre-reinforced sheet material. In another preferred embodiment, a
wind turbine blade according to the invention has a length of at
least 40 m. The ratio of thickness, t, to chord, C, (t/C) is
substantially constant for airfoil sections in the range between
75%<r/R<95%, where r is the distance from the blade root and
R is the total length of the blade. Preferably the constant
thickness to chord is realised in the range of 70%<r/R<95%,
and more preferably for the range of 66%<r/R<95%.
[0088] This may be realised for a wind turbine blade according to
the invention due to the very dense packing of the fibres in areas
of the cross section of the blade, which areas provide a high
moment of inertia. Therefore, it is possible according to the
invention to achieve the same moment of inertia with less
reinforcement material and/or to achieve the same moment of inertia
with a more slim profile. This is desirable to save material and to
allow for an airfoil design according to aerodynamic requirements
rather than according to structural requirements.
BRIEF DESCRIPTION OF THE DRAWINGS
[0089] The invention will now be clarified by way of example only
and with reference to the following FIGURE.
[0090] FIG. 1 shows a diagrammatic cross-sectional view of 3
lay-ups comprising both prepreg and dry fabric layers.
[0091] FIG. 1 shows 3 lay-ups. The top lay-up (100) marked
"infusion only" comprises two layers (102) of a dry fiber material
which comprises LBB1200 fabric. LBB1200 is a
0.degree./+45.degree./-45.degree. triax glass fabric of 1200 gsm
fiber areal weight available from Hexcel Reinforcements
(Villeurbanne, France). The 0.degree. sides of the LBB1200 fabrics
are in contact with one another. On either side of the layers (102)
there is provided a non woven glass mat (104) having an areal
weight of 50 gsm (style designation S5030 from Johns Manville,
Waterville, Ohio). This material allows evacuation of the surfaces
and this results in a good surface finish.
[0092] The second lay-up (110) marked "infusion and prepreg"
comprises a layer of the dry fiber material (112) similar to layer
(102), a prepreg layer (114) and the same nonwoven glass mat layers
(116) and (118) similar to the layers (102,104). The prepreg (114)
consists of the same LBB1200 fabric which is impregnated with M9.1
resin as supplied by Hexcel Corporation. The LBB1200 fabric
contains 32% resin based on the weight of the prepreg. Again, the
0.degree. sides of the LBB1200 fabrics are in contact with one
another.
[0093] Finally, the third lay-up (120) marked "prepreg only"
comprises two layers of the prepreg (122) as used in the second
lay-up (110). Again, the 0.degree. sides of the LBB1200 fabrics are
in contact with one another. The same non-woven glass mat layers
(124) are located on the prepreg layers (122).
[0094] In all lay-ups (100,110,120) the LBB1200 layers are
separated by silicon papers (130) to promote infusion of the resin.
The lay-ups were located with their glass mat side on a flat plate
acting as a mould, and they were covered by a vacuum bag. For
lay-ups (100,110) resin infusion conduits were provided. The stacks
were evacuated and an infusion resin was provided via the infusion
conduits. The infusion resin was prepared from 100 parts by weight
135 RIM as supplied by Hexion with 30 parts by weight of Hexion
RIMH 137 hardener
[0095] The cure schedule was as follows: the temperature was
increased from room temperature to a temperature of 80.degree. C.
at a heat up rate of 1.2.degree. C./min. The temperature was then
held at 80.degree. C. for two hours. This was followed by an
increase in temperature to 120.degree. C. at a heat up rate of
1.2.degree. C./min and the laminate stacks were held at this
temperature for a further hour before they were allowed to cool
down to room temperature.
[0096] The laminates were then tested for their compression
strength in the 0.degree. direction and their compression modulus
in the 0.degree. direction in accordance with standard ISO14126.
18
[0097] The results were as follows (see Table 2 below):
TABLE-US-00003 TABLE 2 Test results. Infusion Prepreg Infusion/
Infusion/prepreg Lay-up Infusion (normalized) Prepreg (normalized)
prepreg (normalized) Compression 690 710 1100 1120 940 890
strength, 0 deg (MPa) Compression 45 47 56 48 51 49 modulus, 0 deg
(GPa)
[0098] The results shown as normalized are based on a resin content
of 35 wt % in relation to the laminate weight.
[0099] Lap shear tests were performed on cured reinforced sheet
material having three different surface finishes.
[0100] The three surface finishes were: [0101] A. Unfinished [0102]
B. Surface sanded with 80 grain abrasive paper [0103] C. Laminate
cured with peel ply which is removed
[0104] Polyspeed C-R150 laminates (Hexcel Corporation) were treated
with one of the surface finishes A-C. Samples were formed by
placing a layer of prepreg comprising 600 g/m.sup.2 unidirectional
carbon fabric and M79 resin between two layers of the surface
finished laminate. The prepreg was then cured to bond the two
laminate layers together.
[0105] The laminates were cut to size and the lap shear strength
was measured in accordance with prEN 6060. Six samples were tested
for each of the surface treatments A, B and C. The mean laps shear
strength is listed in the below Table 3 for each sample set.
TABLE-US-00004 TABLE 3 Lap shear strength results for different
surface treatments. A. Unfinished B. Sanded C Peel Ply Surface
Surface Treated Surface Mean Lap Shear 25.64 28.55 29.36 Strength
(MPa)
* * * * *